1. Field of the Invention
This invention relates generally to the field of pivoting door thrust reversers and more particularly, but not by way of limitation, to an improved thrust reverser which provides improved mechanisms for directing the exhaust efflux to preclude foreign object damage to the engine and interference with the control surfaces of the aircraft and that provides an exhaust nozzle having improved performance in flight.
2. Description of the Prior Art
In order to reduce the landing distance of a jet engine powered aircraft, as well as to increase the margin of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized on the jet engines in order to provide a braking thrust for the aircraft. Such thrust reversers function to reverse the direction of the jet thrust, from a normally rearward direction used for propelling the aircraft in flight, to a generally forward direction for slowing or braking the aircraft.
For low bypass jet engines, the thrust reversers are typical formed by pivoting thrust reverser doors which are pivotally mounded on a fixed structure attached to the engine and to another component of the nacelle. These reverser doors and fixed structure cooperate to form the final nozzle of the gas turbine engine propulsion system. The doors are capable of pivoting between two positions about two spaced parallel axes which are transverse and substantially diametrical with respect to the exhaust of the engine.
The first position finds the doors in a stowed position, out of the direct path of the exhaust forward thrust of the engine. In this position, the doors form, in cooperation with the fixed structure, the exhaust nozzle of the gas turbine engine so that the thrust of the engine is directly rearward, thereby producing forward thrust for the aircraft. In a second position, the doors are pivoted about their pivot axes until their trailing edges abut in a transverse thrust deflecting or deployed position, to block and redirect the engine thrust generally forward and thereby produce the braking thrust for-the engine when needed.
The thrust reversers are generally mounted on a fixed structure. This fixed structure basically serves a dual role. In the forward thrust mode of operation of the jet engine, i.e. when the reverser doors are in the stowed position, the fixed structure forms a part of the envelope of the jet flow and is intended to ensure the best possible flow continuity with the inner skin of the thrust reverser doors.
In the reverse thrust operation, i.e. when the reverser doors are deployed, the fixed structure provides the throat of the nozzle, and defines as well the spacing distance from the thrust reverser doors.
Both of these functions of the fixed structure are important criteria for the proper operation of the jet engine. While in the forward thrust mode, a good flow continuity is essential to the proper forward thrust performance. In addition, the jet exhaust pipe must adequately define the throat area in reverse thrust and the spacing distance in order to satisfy the operational compatibility requirements of the engine and of the thrust reverser when the thrust reverser doors are deployed.
Experience has shown that often thrust reversers tend to favor performance more in the reversing function of operation. But this, unfortunately, is at the expense of the performance provided in the forward thrust mode of operation, meaning that performance degradation during forward thrust is generally associated with the installation of thrust reversers. This is unfortunate since thrust reversers are in operation generally for only 15 to 30 seconds of a flight.
Further, thrust reversers of the prior art have not dealt well with the requirements of deflecting one portion of the reversed exhaust flow upwardly so that it will not adversely effect control surfaces of the aircraft and deflecting a second or other portions of the reversed exhaust flow downwardly and forwardly in a manner that will not cause foreign objects lying on the surface of the landing field to be blown forward so that such objects may be ingested by the engine and thereby cause injury to such engine. Attempts to provide simple inexpensive mechanisms to control the exhaust efflux in the desired manner have not been entirely successful.
Typical pivoting reverser doors generally require a pit or concave portion near their leading edges. This type of configuration does not provide a smooth internal exhaust flow through the nozzle contributing to the degradation in performance during operation in the forward thrust mode. Such doors often have an efflux deflecting member positioned near the leading edge, with such member being pivoted downwardly to deflect the exhaust flow as the door is deployed. Also, problems have been encountered with past thrust reverser door designs in attempting to seal the doors adequately in the stowed position and preclude the exhaust pressure in flight leaking out past the stowed doors to cause drag and marginal performance as well as raising the possibility of having the doors deploy in flight.
Thus, a need exists for a pivoting door thrust reverser that provides a simple, inexpensive, and highly reliable mechanism for the desired forward deflection of the exhaust flow in the deployed mode and to direct portions of the reversed flow so as to avoid interference with control surfaces of the aircraft and to preclude the downwardly directed reversed flow from blowing foreign objects forwardly to a position for ingestion by the engine. A need also exists for a thrust reverser that meets the above criteria while precluding leakage from the reverser unit while in flight and also provides a nozzle that provides a relatively smooth continuous flow for the exhaust of the engine. It is believed that such requirements are met by the instant invention which provides a practical state of the art thrust reverser in an economical manner.